EP1302587A2

EP1302587A2 - Production of suede-finish woven and non-woven fabric with high-elasticity microfiber

Info

Publication number: EP1302587A2
Application number: EP02021713A
Authority: EP
Inventors: David Latini; Omar Teofrasti
Original assignee: Alcantara SpA
Current assignee: Alcantara SpA
Priority date: 2001-10-12
Filing date: 2002-09-25
Publication date: 2003-04-16
Also published as: EP1302587A3; ITMI20012108A1

Abstract

Process for the preparation of microfibrous non-woven fabric with good mechanical and dyeing properties comprising the following stages:

a) preparation of a microfiber constituted in general from polyesters used singularly or in mixtures between them or with nylons 6, nylons 6.6 or other materials normally used in the textile field;

b) preparation, by means of needle-punching, of a felt comprising the microfiber indicated above;

c) impregnation of the felt with polymer binder;

d) mechanical treatment in order to generate the suede effect;

e) dyeing of the non-woven fabric,

in which a polyester constituted partially or totally from repeating monomer units of trimethylene terephthalate (PTT) of formula:

(where n it is a number between 30 and 300) is employed as the polymer for the preparation of the microfibers that constitute the non-woven fabric

Description

The present invention relates to a production process for suede-finished microfibrous woven and non-woven fabrics characterized by high formability and elasticity, which can be dyed at relatively low temperatures and have good color characteristics (fastness of the color to washing, abrasion and light).
In particular, the present invention refers to the employment of a particular polymer that, when used as the microfiber component in the preparation of the felt of the non-woven fabric, gives advanced properties to the finished product.
Processes are known for the preparation of non-woven fabrics that have the appearance and the characteristics of suede leather and that, moreover, have properties of resistance against mechanical abrasion, the action of solvents, and attack by aggressive chemicals in general, which are superior to those of the natural product. These processes are described in many documents of the state of the art and in particular in Patent US-A-3.531.368 and in Italian Patents 905.222, 921.871 and in general involve the following stages:
a) preparation of a microfiber constituted typically of nylon 6 or nylon 6.6, polyethylene terephthalate or other materials normally used in the textile field;
b) preparation, by means of needle punching of a felt comprising the aforementioned microfiber
c) impregnation of the felt with polymer binders,
d) mechanical treatment to generate the suede effect;
e) dyeing the non-woven fabric.
The list of stages reported is considerably simplified in so far as many other important stages are involved, both after stage d) or between the above-mentioned stages. In particular, the preparation of the microfiber, which is a critical stage in the preparation of the microfibrous non-woven fabric, can be favorably achieved by means of co-extruding the chosen polymer with another polymer through a spinneret with particular holes in such a way that the two-component fiber has a cross-section where a bundle of microfibers are surrounded by the co-extruded polymer (islands-in-the-sea). Several treatments of the extruded fiber provide for the separation of the microfiber from the polymer that surrounds it.
The products obtained with the series of stages defined above and described in some of the patents cited, have good physical-mechanical and textile characteristics. However, it must be noted that the end product, comprising impregnated fibers (microfibers) in a polymer binder that confers a suede-leather appearance on it and is generally polyurethane, has the defects and advantages of its components and, in particular, of the microfiber used.
As has been pointed out above, the polymers commonly used for the microfiber production are polyethylene terephthalate (PET) and Nylon (6 or 6.6). PET offers the advantage to guaranteeing good dyeing characteristics to the finished product -- even though the dyeing process must be carried out at high temperatures (> 120 °C) which reduces the mechanical characteristics.
Moreover, the intrinsic properties of PET do not permit products with high levels of formability and elasticity to be obtained.
The present invention relates to a polymer that can be transformed into a fiber or microfiber that does not have the aforementioned defects of PET. In particular, the fiber or the microfiber used as a constituent of suede-finished fabrics according to the present invention confers characteristics of considerable formability and elasticity on these. In addition, the raw product shows optimum dyability even with treatment carried out at relatively low temperatures, thus maintaining the good mechanical characteristics of the intermediate before dyeing, and, once dyed, has colour properties of the level of PET-based products.
The object of the present invention is achieved by using a polyester consisting of a repeating monomer unit of trimethylene terephthalate(PTT), of formula:
(where n is a number between 30 and 300) as the polymer for the preparation of the microfibers that constitute the non-woven fabric.
The PTT has high formability as well as high elastic recovery. This means that products prepared with PTT fibers can be considerably distorted, but, once the force causing the deformation is removed, they resume their original shape. This mechanical property is particularly appreciated in the field of use of the suede-finished microfibrous non-woven fabric of the present invention, particularly in the technological area of interior coverings of automobiles, furniture and clothing.
As pointed out above, PTT fibres can be dyed using dye treatments at temperatures somewhat lower than those demanded by PET, especially the fibers and the microfibers, therefore products obtained from PTT, as well as having good dyability, assure retention of mechanical characteristics of the raw product.
Polytrimethylene terephthalate is readily avilable nowadays, and can be obtained by reaction of terephthalic acid or its ester with propylene glycol. Many methods are described in the literature for the preparation of polymers and co-polymers of PTT.
The spinning technologies used for the preparation of fibers or microfibers containing PET can also be used to obtain PTT microfibers and twin-component fibers.These have a twofold purpose:
to guarantee continuity of spinning
to give a product which can resist the mechanical stresses imposed by the process of transformation into felt (carding, drawing) or by working on the loom.
The aforesaid objectives can be conventionally reached through the use of "conjugated" fibers, that is fibers of higher denier (> 1 den) obtained by co-extruding two or more polymers with different chemical composition. The coextruded fibers once transformed into staple by means of drawing, crimping and cutting, are subjected to carding and needle-punching to be transformed into felt or are processed to give wovens. Only at this point is the microfiber generated by separating the two polymers with appropriate mechanical or chemical treatment (heating, extraction with solvent, selective swelling, use of high pressure water-jets). Mono-component spinning of low denier fibers or microfibers can also be proceeded to, followed by multi-layer distribution technology (as for the production of paper from cellulose microfiber) and water punching.
In all cases it is possible to insert an internal textile support (fabric or knit) to the structure by means of lamination and needle-punching . Use of the PTT allows products to obtained with high elasticity (equal or superior to that of products made of Nylon) together with optimum dyeing properties, operating in relatively mild dyeing conditions; this in virtue of the intrinsic characteristics of the polymer, which can be summarized as follows:
high formability under stress added to elastic behavior
low glass transition temperature (50 °C against 80 °C for PET) that guarantees low dyeing temperatures
good affinity for dispersed dyestuffs, with consequent improvement of the dyeing characteristics.
The complete production procedure for the products which are the object of the present invention is described below with reference to the sole diagram in which some spinning row sections are reported by way of example which should not be interpreted as limiting.
a) Production of the twin-component fiber is obtained by means of co-extrusion of the polymer that comprises microfiber (PTT) and of one or more auxiliary members, which can be modified polyesters, polyamides, polystyrenes, and in general all the spinnable polymers that can be removed from the twin-component fiber and free the microfiber of PTT. The microfiber can be separated from the co-extruded fiber by any known method, either mechanical or physical. Typically, the removal of the co-extrusion polymer is achieved due to its greater solubility with respect to PTT in determined solvents. Appropriate plasticizing agents can be added to the auxiliary component in order to optimize the rheological characteristics. The ratio between the PTT and the auxiliary polymer is advantageously between 20/80 and 80/20. The spinning fiber is between 8 and 15 den. The fiber is then subjected to stretching (stretching ratio between 1,5 and 4) in one or two stretching steps. One proceeds next to crimping and cutting to give the staple.
b) preparation of the felt with the twin-component fiber
c) impregnation of the felt with polyvinyl alcohol (PVA) PVA characterized by saponification percentage values between 80% and 99,9% can be used.The PVA application process is preceded by a shrinkage step executed in warm water at a temperature between 80 and 100°C. Said shrinkage can also be carried out in the polyvinyl alcohol impregnation bath operating at the same temperature. The percentage of PVA in the impregnated product varied from 10 to 35%.In the case of high saponification products, the drying of the PVA after impregnation must be followed by a heat treatment at 180-220°C to improve the water insolubility characteristics. The insolubility of the PVA in water can also be increased by adding appropriate reticulating agents such as titaniums, zirconates, and boric acid.
d) Separation of the microfiber from the auxiliary component This operation can be done before or after the PVA application.The auxiliary component can be caused to dissolve or swell by using, depending on its characteristics, organic solvents (halogenated or aromatic hydrocarbons, alcohols, ketones, carboxylic acids, phenols) or neutral, acidic or alkaline aqueous solutions. Alternatively, heat or mechanical (fibrillation) treatment can be carried out, or high pressure (up to 400 bar) water jets can be used to separate the microfiber.
e) Impregnation with polyurethane The polyurethane used can either be dispersed in water or dissolved in an organic solvent(dimethylformamide, dimethylacetamide) .Polymers containing aromatic or aliphatic isocyanates, and polyols such as polyethers, polyesters, polycarbonates and acrylics are used. External (anionic, cationic, or non-ionic surfactancts), or anionic- or cationic-type inner (Co-monomers ) emulsifiers can be used for the polymers dispersed in water. In both cases (organic solution or aqueous dispersion) the polymer is extended with aliphatic, aromatic (generated by hydrolysis of the isocyanates with water) amines, or aliphatic or aromatic glycols.An appropriate crosslinking agent can be added to the product in aqueous dispersion to improve its mechanical characteristics.The polyurethane content of the finished product is from 15 to 45%.
f) The polyurethane coagulated in organic-solvent/aqueous solutions with solvent concentration of from 0 to 50% and temperatures from 20 to 50°C is successively oven-dried. Alternatively the product can be fixed by means of direct drying in an oven.In order to optimize the distribution of water-borne polyurethane, the drying process can be carried out in suitable microwave ovens and can be preceded by a steaming phase in an oven fed with saturated steam. The drying or coagulating process can be followed by high-temperature heat treatment in order to enable crosslinking of the polyurethane.
g) Extraction of the polyvinyl alcohol in water at temperatures between the 70 and 100°C. b)
h) Application of silicone emulsion and anti-static agents for impregnation (up to 1% of the solid in intermediate sheet).
j) Splitting along the section and buffing.
k) Dyeing with dispersed and/or pre-metallized dye.
i) Application of finishing (softening, anti-static, fire-proofing) agents.
Non-woven fabric with better mechanical properties can be obtained by lamination of two external layers of PTT-base staple with an inner fabric support in knit or woven cotton, acrylic or polyester, or by heat-bonding the finished product with a woven fabric support. Whenever the textile support is intrinsically elastic (e.g. uses polyurethane fibers) the formability and elastic properties given by the microfiber to the finished product are further improved.
As an alternative to the aforesaid process, woven fabrics can be produced by starting from the stretched fiber. Microfibres are then generated from the above mentioned wovens according to the methods already described, and the process is completed by polyurethane application, mechanical treatment to upgrade the surface (suede effect), dyeing and finishing.
The use of binary or tertiary mixtures of PTT with other polyesters (PET, PBT) makes good levels of elasticity attainable. The aforesaid mixtures can be produced in one or more of the methods reported below:
1. Melt mixing of various polyester granules by weight ratios varying from 0 to 95%.
2. Mixing in the stretch-crimp phase of twin-component fibers having single polyesters as the base component (weight ratios between 0 and 95%).
3. Mixing of single-polyester base staples before carding (weight ratios between 0 and 95%).
EXAMPLE 1 (comparison of standard PET base product and PTT base product). A fiber is prepared in staple formed from microfibers of the component base ( PET, PTT respectively) in a polystyrene matrix ("island-sea" fiber obtained using a spinneret having the section identified as 1 in the figure) through a spinning process that has the following steps:
Drying under vacuum (20 mmHg) of polyester granules at 100°C for 6 hours, then at 155°C for 8 hours.
Extrusion and spinning from spindle in the following base conditions

Base Component Extrusion Temperature(°C) Polymer Temperature (°C) Winder Speed (m/min) Fiber titre (den)

PET 260 - 290 285 1700 9.8

PTT 235 - 265 262 1700 9.8
In particular, the fiber is composed of 57 parts by weight of PET and 43 parts polystyrene Finishing of spinning fibers: stretch ( stretch ratio = 2.5 at a stretch temperature of 115°C) - crimping - drying - cutting, giving a staple with the following characteristics:
Weight = 3.9 den;
Length = 51 milimeter;
Curl = approximately 4/cm
Mechanical characteristics of the stretched fiber

Base Component Tenacity (g/den) Elongation at break (%) Shrinkage in water at 100 °C (% area)

PET 2.2 65 17

PTT 1.9 90 28
After extraction of the sea component with trichloroethylene the mechanical characteristics of the fiber are the following

Base Component Tenacity (g/den) Elongation at break (%)

PET 4.3 78

PTT 4 109
With the staple obtained a first felt is produced by carding and successive needle-punching is proceeded to until a finished felt is obtained with density of 0,2 g/cm3.
The felt is then impregnated with a polyvinyl alcohol (PVA) solution in water (12% by weight) at high temperature (95°C) in order to carry out shrinkage.
The product is dried in an oven and then the sea component (polystyrene) is dissolved with trichloroethylene.
The following step is impregnation of the intermediate product with polyurethane in dimethylformamide (12.5% by weight) solution and the successive coagulation in aqueous solution.
The polyvinyl alcohol is extracted with water at 80°C and a mixture of silicone and an antistatic agent (quaternated polyalkylene-polyamide) in aqueous dispersion (0.2% by weight for both) is applied to the wet product, which is finally dried in an oven.
The piece is finally cut in two in the section, buffed and colored with dispersed dyes. Finished products made from PTT have deformation values under dynamic load (50 N) increased by 40% on average compared to standard (PET).

EXAMPLE 2 (comparison between standard PET base product and PTT base product obtained without using organic solvents).

Also in this case the fiber has the cross section 1 as reported in figure 1 and is composed of island base components (PET, PTT) in a matrix of soluble co-polyester in aqueous alkaline solutions (TLAS) with an island to sea weight ratio of 57/43.
The drying is carried out as reported in Example 1.
The main operating conditions of extrusion are listed below:

Base Component Extrusion Temperature (°C) Polymer Temperature (°C) Winder Speed (m/min) Fiber Titre (den)

PET 260 - 290 285 1400 13.6

PTT 235 - 265 262 1400 13.6
The fiber is stretched at a temperature of 75 °C, in two steps, for a stretch ratio of 3,5. The final staple has the same weight, length and curl characteristics as reported in example 1.

The mechanical characteristics of the stretched fiber are:

Base component	Bicomponent fibre	Polyester microfibre
	Tenacity (g/den)	Elongation at break (%)	Shrinkage in water at 100°C (%)	Tenacity (g/den)	Elongation at break (%)
PET	2.8	50	26	4.6	65
PTT	2.5	75	35	4.4	96

The staple is carded and successively needle-punching until a felt of density 0,22 g/cm³ is obtained.
The felt then undergoes a shrinkage process in water at 95°C in order stabilize the structure and its density increases to 0,33 g/cm3.
The felt is then impregnated with an 8% by weight aqueous solution of high saponification polyvinyl alcohol (HS-PVA with saponification value > 99.5% molar). After drying (at 100°C) the product is thermally treated (4 minutes at 180°C) in order to reduce the solubility in water of the HS-PVA. A polyurethane in aqueous emulsion (2.5% by weight) with to an appropriate thickening-reticulating agent of blocked isocyanate type (10% by weight of polyurethane) is then applied the product is dried at 100°C, then thermofixed at 150°C.
The next step is the dissolving of the sea component in Sodium Hydroxide solution in the following conditions:
NaOH Concentration = 10% by weight
Temperature of the bath = 60 °C
Time of treatment = 20 minutes
The raw product is then impregnated with polyurethane in aqueous emulsion (12.5% by weight) containing 5% of blocked isocyanate reticulating agent, followed by the drying and the thermosetting at 160°C.
The polyvinyl alcohol is extracted with water at 90°C and a mixture of silicone and an antistatic agent (quaternated polyalkylene-polyamide) in aqueous dispersion (0.2% by weight for both) is applied to the damp product which is finally dried in an oven.
The piece is finally cut in two in the section, buffed and colored with dispersing dyes. Also in this case the finished products made from PTT have deformation values under dynamic load (50 N) increased by 40% on average compared to standard (PET).

Claims

Process for the preparation of microfibrous non-woven fabric with good mechanical and dyeing properties comprising the following stages:

a) preparation of a microfiber constituted in general from polyesters used singularly or in mixture between them or with nylon 6, nylon 6.6 or other materials normally used in textile field;

b) preparation, by means of needle-punching, of a felt comprising the microfiber indicated above;

c) impregnation of the felt with binding polymer;

d) mechanical treatment in order to generate the suede effect;

e) dyeing of the non-woven fabric,

characterized in that the polymer employed for the non-woven fabric microfibre preparation is a polyester constituted partially or totally from repeating monomer units of trimethylene terephthalate (PTT) of formula:
(where n is a number between 30 and 300)
Process for the preparation of non-woven microfibrous fabric with good mechanical and dyeing properties according to Claim 1, characterized by the microfibers of PTT deriving from conjugated fibers obtained by co-extruding polytrimethylene terephthalate with one or more polymers that are subsequently separated.
Process according to Claim 2, characterized in that the polymer that is co-extruded with the polytrimethylene terephthalate being polystyrene.
Process according to Claim 2, characterized in that the polymer that is co-extruded with the polytrimethylene terephthalate is a co-polyester soluble in alkaline solutions, having the base structure of PET and modified by means of the introduction of isophtalic-5 sodium sulphonate acid.
Process according to Claim 1, characterized by the conjugated fiber being constituted by microfibers of PTT combined with the co-extrusion polymer to give fibers of special section in which the ratio by weight between the PTT and the co-extrusion polymer goes from 80/20 to 20/80.
Process according to Claim 1, characterized by the co-extrusion polymer being separated from the PTT by means of dissolving in a solvent.
Process according to Claim 1, characterized by the co-extrusion polymer being separated from the PTT by means of heat or mechanical treatment or by subjecting fibers to highpressure water jets.
Process according to one or more of the previous Claims, characterized by the felt constituted by microfibers of PTT being impregnated with polymer binder before or after the separation of the co-extrusion polymer.
Process according to Claim 8 characterized by the polymer binder being Polyvinyl alcohol (PVA).
The use of the polytrimethylene terephthalate for the preparation of microfiber useful in the production of microfibrous suede-finished non-woven fabric.
Microfibre of polytrimetilene terephthalate obtained from composite fibers of trimethylene terephthalate and polystyrene by means of separation of the latter with selective solvent.
Process for the production of suede-finished non-woven fabric using microfibers of politrimetilene terephthalate impregnated with polyurethane binder.